The Effect of Fasting on Body Composition Assessment in Hospitalized Cancer Patients

Guidelines for bioelectrical impedance analysis (BIA) recommend fasting before measurements, but how it affects the outcomes is unclear. This descriptive, before-and-after study examines the effect of fasting on BIA results and its impact on the diagnosis of malnutrition in hospitalized cancer patients. Fifty-three oncology patients (admitted in January-March 2020) were consecutively enrolled regardless of their nutritional status. Patients were assessed by the same dietician 24-48 h after admission, following the usual clinical practice. The measurements were taken after 12-h fasting (fasting state) and 60-90 min after breakfast (non-fasting state). Bioimpedance parameters (resistance [R], reactance [Xc], phase angle [PA]) and body composition indices (free-fat mass index [FFMI] and appendicular skeletal muscle index [ASMI]) were calculated. On average, R values did not significantly differ between fasting and non-fasting states (mean difference: +1.82 Ω; p = 0.64). The non-fasting Xc and PA were reduced (mean differences: -1.55 Ω, p = 0.93 and 0.09°, p = 0.82, respectively). Fasting and non-fasting FFMI and ASMI were similar (mean differences: -0.13 kg/m² (p = 0.5) and -0.10 kg/m² (p not calculated)). These results suggest that BIA does not require fasting, facilitating its routine use in hospitalized cancer patients.